Trane TUH1B080A9H31A Error Code 3 Flashes: Pressure Switch Error
What Does Code 3 Flashes Mean?
The 3-flash code on the Trane TUH1B080A9H31A indicates a pressure switch error. The pressure switch failed to close or opened during operation, which means the furnace cannot confirm that exhaust gases are being safely vented outside your home. The furnace will not ignite until this issue is resolved.
The pressure switch is a safety device connected to the inducer (draft) motor housing by a small rubber hose. When the inducer motor runs, it creates negative pressure that pulls the pressure switch closed, confirming proper airflow through the vent system. If this switch does not close or opens during a heating cycle, the control board shuts down ignition immediately.
The most common cause is a blocked exhaust vent pipe, especially during winter when snow and ice can obstruct the vent termination outside your home. Other causes include a faulty pressure switch or a failing inducer motor that cannot generate enough suction.
Common Causes
| Cause | Likelihood | DIY? |
|---|---|---|
| Blocked or restricted vent pipe | Most common | ✗ Call a pro → |
| Faulty pressure switch | Common | ✗ Call a pro → |
| Failed inducer motor | Uncommon | ✗ Call a pro → |
When to Call a Professional
Contact a licensed HVAC technician if:
- The vent pipes appear clear but the 3-flash code persists
- The inducer motor sounds unusually loud, rattles, or does not start at all
- You notice the pressure switch hose is cracked, disconnected, or has water in it
- The code returns intermittently, especially on windy days
✓ Verified against manufacturer service manual — March 2026